MORPHOLOGY AND TAXONOMY OF MASTIGOPHORA 279 



A large, single nucleus more like that of Dinoflagellates than other 

 protozoan nuclei, undergoes a characteristic process of mitosis 

 during division (Fig. 52, p. 101). 



Order IV. PHYTOMONADmA, Blochmann. 



The green flagellates included in this order are the most plant- 

 like of all Protozoa. Their closest affinities are probably with the 

 Chlorophyceae through the algse. The chromatophores are colored 

 with grass-green chlorophyll while hematochrome (karotin) in some 

 cases masks the green. Nutrition therefore, is typically holophytic 

 except in the Polytomidse where chromatophores are frequently 

 absent and nutrition is saprozoic. As a result of their method of 

 nutrition assimilation products are almost invariably starch. The 

 chromatophores are usually single, large, cup-shape, and fill the 

 greater part of the cell, while distinct pyrenoids are usually present. 



The individual monads are small, spheroidal, or spindle-shape 

 organisms with membranes of cellulose or pektine and are never 

 metabolic. Flagella vary in number from 1 to 2 (rarely 4 to 8) and 

 protrude from the anterior end through a definite pore in the 

 membrane. The vacuole system is simple, usually consisting of a 

 number of contractile vacuoles grouped at the anterior end. The 

 nucleus is distinct, usually near the center of the cell and divides 

 in such a plane that longitudinal di^■ision of the cell is assured. This 

 occurs within the cellulose membrane which is left as an empty shell 

 when the daughter cells emerge. Repeated divisions frecpently 

 occur in which case the successive division planes are at right angles 

 to one another. Palmella-stages, either intermediate or terminal in 

 the life history, are frequent while colony formation is highly char- 

 acteristic, particularly in the Volvocida?. Encystment stages in 

 which the monads retract from the cellulose membranes are wide- 

 spread. 



Sexual processes are highly characteristic and involve more or 

 less specialized sexually differentiated individuals or colonies with 

 isogamous or anisogamous gametes (see p. 503). 



Family 1. Polyblepharidae, Dangeard.— These forms differ from 

 the majority of other Phytomonadida in the absence of cellulose 

 membranes and in the tendency to metaboly. They represent 

 connecting forms with other colored flagellates and are more gen- 

 eralized than other members of the group. This is shown by the 

 absence of sexual processes and by the larger number of flagella 

 possessed by individuals. Tj'jjical genus Pyrcnnimonas. 



Family 2. Phacotidse, Poche.^Phytomonads with a bivalve 

 shell, or at least a membrane which splits easily to form two lens- 

 like halves as in Phacatus lenticularis. Two flagella pass through a 

 canal to the outside. Chromatophores and stigmata are character- 



